1. Field of the Invention
The present invention relates to computer networks and to interface devices for connecting host computers to networks. More particularly, the present invention relates to managing transmission of traffic by network interface cards (NICs) with a plurality of virtual paths, in network connected systems.
2. Description of Related Art
Computer systems often include network interfaces that support high speed data transfers between a host computer and a data network. Such computer systems include an adapter commonly termed a Network Interface Card, or Chip, (NIC). Such adapters typically connect to a host processor via a bus such as the well known PCI, PCMCIA etc.
NICs typically have semiconductor read-write random access memory arrays (RAM) so that data transfers to and from the host memory are anisochronous to transfers to and from the network. Such RAM is typically arranged as a transmit first-in-first-out (FIFO) buffer and a receive FIFO buffer. Thus, packets coming into the NIC, from the host memory, are stored in a transmit FIFO buffer pending transmission onto the network. Conversely, packets coming into the NIC from the network are stored in a receive FIFO buffer, pending transfer into the host memory.
As computer networks are adapted to carry a variety of types of traffic, network protocols are being developed to support variant processing of packets as they traverse the network. Thus, priority packets are developed which are suitable for carrying real-time video or audio signals. These priority packets are processed ahead of other packets in sequence when possible to improve the throughput and reduce the latency of processing for this class of packet. Also, network security is supported for some types of packets. Thus, the Internet security IPSec protocols are being developed. (Request For Comments, 2401 Security Architecture for the Internet Protocol, Internet Engineering Task Force). According to security protocols, the payload and/or the header and other control data associated with the packet are protected using authentication and encryption processes. Accordingly, a variety of priority schemes and other schemes involving processing of packets according to particular processes like encryption through the network have been developed.
The FIFO structure in network interface cards suffers the disadvantage that it is inflexible in the sequence of processing of packets being transferred through the interface, that is, a FIFO structure supports only sequential data transfer. Each packet being loaded will be unloaded through the same sequence determined by the order of receipt of the packet into a typical FIFO-based network interface. Therefore, the processing of packets according to protocols which may benefit from processing out of order must be executed before the packets are delivered to the network interface, or after the packets leave the network interface. The U.S. patent application Ser. No. 09/451,395, entitled “FIFO-BASED NETWORK INTERFACE SUPPORTING OUT-OF-ORDER PROCESSING”, filed 30 Nov. 1999, inventors Chi-Lie Wang, Li-Jau Yang, Ngo Thanh Ho, referred to above describes one approach to improving the flexibility of network interface devices.
Accordingly, it is desirable to provide techniques for improving the flexibility of network interfaces.